1. Field of the Invention
The present invention generally relates to light amplifier devices, and more particularly to a light amplifier device having an optical amplifier medium such as an optical fiber with a rare-earth element doped.
2. Description of the Related Art
FIG. 1 is a diagram of a conventional light amplifier device having an optical fiber with a rare-earth element doped. A light amplifier device 9 shown in FIG. 1 includes an optical fiber 5 with a rare-earth element doped. For example, the optical fiber 5 is an erbium-doped optical fiber. A signal light 9A is applied to the erbium-doped optical fiber via an optical isolator 1a and an optical multiplexer 2a, which is also called a wavelength-division multiplexing (WDM) coupler. An exciting light (pumping light) 9C is emitted from an exciting light source 3a, and is forwardly applied to the erbium-doped optical fiber via the optical multiplexer 2a. An exciting light source 3b emits another exciting light 9C, which is backwardly applied to the erbium-doped optical fiber 5 via an optical multiplexer 2b. The exciting lights 9C cause an inverted distribution of energy in the erbium-doped optical fiber 5. A control circuit 4 controls the output level and timing of the exciting lights 9C emitted from the exciting light sources 3a and 3b.The erbium-doped optical fiber 5 amplifies the signal light 9A due to induced emission. The amplified light signal passes through the optical multiplexer 2b and an optical isolator 1b.
Generally, the above structural components of the light amplifier device 9 are module components which stand alone therein. That is, in the device there are separately provided the erbium-doped optical fiber 5, the exciting light sources 3a and 3b, the optical multiplexers 2a and 2b and the optical isolators 1a and 1b. Hence, it is very difficult to realize down sizing of the light amplifier device 9. The modules are optically connected together by optical fibers, which are connected to the modules by a splice method (which is a thermal fusion method in which the optical fibers are heated). It will be noted that the connecting work is very troublesome. As the number of optical components of the light amplifier device 9 increases, the yield of the production decreases and the reliability degrades.
Further, there is another problem resulting from a requirement in which the radius of curvature of the optical fibers connecting the optical components together is equal to or greater than 30 mm. This requirement makes it difficult to arrange the optical fibers in the light amplifier device 9A (fiber homing) and prevents down sizing of the device 9A.